"I charge the leaders of this Government with the moral crime of ecocide. I trust that in due course that they stand accountable before the children of this world, the children of John Key, the grandchildren of Tim Groser and mine."

He went further: "The leaders of this government ... are committing us to purgatory and thence to hell. Purgatory is the next decade, and hell the decade after."

Ecocide, the environmental equivalent of genocide, has been written into domestic law in 10 countries and related to serious, lasting damage to ecosystems.

Dr Graham argued that it was daft to remove agriculture - which produced nearly half of New Zealand's emissions - from the ETS while polar ice caps were melting rapidly.

National MPs immediately objected to Dr Kennedy's speech.

MP Maurice Williamson told off the Speaker for not intervening: "When a member gets up and lays a charge of ecocide and you're asking us to sit here and tolerate that, Sir? I find that offensive."

Former Environment Minister Nick Smith pointed out that global temperatures were expected to be 0.3C higher in 10 years' time. "It is a gross exaggeration to talk about hell on earth," he said.

The controversial amendments were passed into law yesterday by a vote of 61 to 58, with National, Act and United Future in favour and Maori, Labour, Greens, New Zealand First and Mana against.

The Maori Party initially backed the bill but its support wavered as the price of carbon collapsed in the last year.

Iwi, as major forestry owners, held a third of the New Zealand-issued carbon credits, which lost an estimated $500 million in value as the global price plummeted.

This led to Opposition calls to limit importation of cheap carbon credits.

Climate Change Minister Tim Groser said yesterday the law change ensured the cost of the ETS did not impact unreasonably on New Zealand households and businesses.

EcocideTen countries in South America, Asia and eastern Europe have adopted a law of ecocide. The environmental equivalent of genocide, it has been defined as "the mass damage, destruction or loss of ecosystems of a given territory, whether by human agency or by other causes, to such an extent that peaceful enjoyment by the inhabitants of that territory has been severely diminished".